CN117296172A - fuel cell system - Google Patents

fuel cell system Download PDF

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Publication number
CN117296172A
CN117296172A CN202180097869.0A CN202180097869A CN117296172A CN 117296172 A CN117296172 A CN 117296172A CN 202180097869 A CN202180097869 A CN 202180097869A CN 117296172 A CN117296172 A CN 117296172A
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CN
China
Prior art keywords
anode
gas
fuel cell
flow path
temperature
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Pending
Application number
CN202180097869.0A
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Chinese (zh)
Inventor
筱木俊雄
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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Publication of CN117296172A publication Critical patent/CN117296172A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04858—Electric variables
    • H01M8/04925—Power, energy, capacity or load
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04014—Heat exchange using gaseous fluids; Heat exchange by combustion of reactants
    • H01M8/04022—Heating by combustion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04037—Electrical heating
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04097—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with recycling of the reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
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    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
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    • H01M8/04119—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying
    • H01M8/04156—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying with product water removal
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04223—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
    • H01M8/04225—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells during start-up
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    • H01M8/04223—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
    • H01M8/04228—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells during shut-down
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    • H01M8/04223—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
    • H01M8/04268—Heating of fuel cells during the start-up of the fuel cells
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    • H01M8/04302—Processes for controlling fuel cells or fuel cell systems applied during specific periods applied during start-up
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    • H01M8/04303—Processes for controlling fuel cells or fuel cell systems applied during specific periods applied during shut-down
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0432—Temperature; Ambient temperature
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0432—Temperature; Ambient temperature
    • H01M8/04343—Temperature; Ambient temperature of anode exhausts
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0432—Temperature; Ambient temperature
    • H01M8/04365—Temperature; Ambient temperature of other components of a fuel cell or fuel cell stacks
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0432—Temperature; Ambient temperature
    • H01M8/04373—Temperature; Ambient temperature of auxiliary devices, e.g. reformers, compressors, burners
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
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    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
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    • H01M8/04701—Temperature
    • H01M8/04738—Temperature of auxiliary devices, e.g. reformer, compressor, burner
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04746—Pressure; Flow
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
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    • H01M8/04746—Pressure; Flow
    • H01M8/04761—Pressure; Flow of fuel cell exhausts
    • H—ELECTRICITY
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    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
    • H01M8/0618—Reforming processes, e.g. autothermal, partial oxidation or steam reforming
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

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  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Fuel Cell (AREA)

Abstract

The fuel cell system is provided with: a steam generator for heating water to generate steam; a reformer for reacting steam with hydrocarbon to generate reformed gas containing hydrogen; a fuel cell stack having an anode and a cathode, and generating electric power by an electrochemical reaction of a reformed gas supplied to the anode and an oxidant supplied to the cathode; and an ejector that uses water vapor as a driving fluid, and that supplies at least one of a hydrocarbon-containing raw material and an anode recycle gas obtained by recovering a part of an anode off-gas discharged from the anode to the reformer, the vapor generator including: an evaporation flow path through which water flows; an anode off-gas flow path thermally connected to the evaporation flow path, the anode off-gas flowing; and an auxiliary heating device for heating water, wherein the anode off-gas flow path and the auxiliary heating device are opposed to each other across the evaporation flow path.

Description

Fuel cell system
Technical Field
The present disclosure relates to a fuel cell system provided with a vapor generator.
Background
Patent document 1 describes an evaporator for a reformer provided in a preceding stage of the reformer in a fuel cell system. In this reformer evaporator, a burner is provided as a heat generating portion. The evaporation tube is spirally wound around the outer periphery of the heat generating portion. The heat energy generated by the combustion of the burner is transferred to the evaporating tube. Thereby, the water in the evaporation tube is gasified.
Prior art literature
Patent literature
Patent document 1: japanese patent application laid-open No. 2004-14141
Disclosure of Invention
However, in the reformer evaporator of patent document 1, in order to continuously supply vaporization heat to water, it is necessary to continuously supply combustion gas to the burner. Therefore, in the fuel cell system using the reformer evaporator of patent document 1, there is a problem that energy efficiency becomes low.
The present disclosure has been made to solve the above-described problems, and an object thereof is to provide a fuel cell system capable of obtaining higher energy efficiency.
The fuel cell system according to the present disclosure includes: a steam generator for heating water to generate steam; a reformer configured to react the steam with hydrocarbon to generate a reformed gas containing hydrogen; a fuel cell stack having an anode and a cathode, generating electric power by an electrochemical reaction of the reformed gas supplied to the anode and an oxidant supplied to the cathode; and an ejector that uses the steam as a driving fluid and supplies at least one of a raw material including the hydrocarbon and an anode recycle gas obtained by recovering a part of an anode off-gas discharged from the anode to the reformer, the steam generator including: an evaporation flow path through which the water flows; an anode off-gas flow path thermally connected to the evaporation flow path, the anode off-gas flowing through; and an auxiliary heating device for heating the water, wherein the anode off-gas flow path and the auxiliary heating device are opposed to each other across the evaporation flow path.
According to the present disclosure, in the fuel cell system, higher energy efficiency can be obtained.
Drawings
Fig. 1 is a system diagram showing the structure of a fuel cell system according to embodiment 1.
Fig. 2 is a cross-sectional view showing an internal structure of a vapor generator in the fuel cell system according to embodiment 1.
Fig. 3 is a cross-sectional view showing the structure of an anode off-gas flow path inlet and its surroundings in the steam generator according to modification 1-1 of embodiment 1.
Fig. 4 is a cross-sectional view showing the structure of an anode off-gas flow path inlet and its surroundings in the steam generator according to modification 1-2 of embodiment 1.
Fig. 5 is a cross-sectional view showing the structure of an anode off-gas flow path inlet and its surroundings in the steam generator according to modification 1-3 of embodiment 1.
Fig. 6 is a system diagram showing the structure of the fuel cell system according to embodiment 2.
Fig. 7 is a cross-sectional view showing an internal structure of a vapor generator in the fuel cell system according to embodiment 2.
Fig. 8 is a system diagram showing the structure of the fuel cell system according to embodiment 3.
Fig. 9 is a cross-sectional view showing an internal structure of a steam generator according to modification 3-1 of embodiment 3.
Fig. 10 is a system diagram showing the structure of a fuel cell system according to embodiment 4.
(symbol description)
1: a fuel cell stack; 1a: an anode; 1c: a cathode; 1e: an electrolyte; 2: reformer (reforming section); 3: a burner; 4: a vapor generator; 4a: a central shaft; 4b: an outer peripheral wall (flow path wall); 4b1: an inner wall surface; 4c: an inner peripheral wall; 4d: a partition wall; 4e: an upper wall; 4f: a lower wall; 5: a water separator; 6: a water piping; 7: an oxidant heat exchanger; 8: a water pump; 9: an ejector; 10: a heat recovery cooler; 14: a water treatment device; 18: a blower; 19: a raw material pretreatment device; 20: a water vapor temperature sensor; 21: an anode exhaust gas temperature sensor; 22: a stack temperature sensor; 23: a circulating heat exchanger; 24: a reformer temperature sensor; 41: an outer peripheral space; 42: an inner peripheral space; 50: an auxiliary burner; 90: a control unit; 100: a fuel cell system; 200: a raw material system; 201: reforming a feed system; 202: a fuel gas system; 203: an oxidant system; 204: a cathode exhaust system; 205: a reformed gas system; 206: an anode exhaust system; 207: an anode recycle gas system; 208: recirculating the combustion gas system; 209: an anode recycle gas system; 210: a circulating water system; 211: a water vapor system; 214: a heat recovery system; 215: a combustion exhaust system; 216: an auxiliary combustion fuel system; 217: an auxiliary combustion fuel system; 218: an auxiliary combustion fuel system; 221: a recovery branching section; 301: an evaporation flow path; 301a: a heat transfer tube; 301b: an evaporation flow path inlet; 301c: an evaporation flow path outlet; 302: an anode off-gas flow path; 303: an auxiliary heating device; 304: a dew accumulation space; 305: a dew water discharging pipe; 305a: a dew water discharging valve; 306: a heat transfer promoting member; 307: an anode off-gas flow path inlet; 307a: an inflow tube; 307a1: an end face; 308: an anode off-gas flow path outlet; 308a: an outflow tube; 311: a recirculated combustion gas flow rate adjustment valve (shut-off section); 312: a recirculated combustion gas flow meter; 313: a dew-water guide plate; 313a: an end portion; 313b: the other end part; 313c: a through hole; 314: a combustion exhaust gas flow path; 315: a partition wall; 316: a1 st flow path member; 316a: a groove; 317: a 2 nd flow path member; f00: raw materials; f01: raw materials; f02: a fuel gas; f03: an oxidizing agent; f04: cathode exhaust gas; f05: reforming a gas; f06: anode off-gas; f07: anode recovery gas; f08: recirculating the combustion gases; f09: an anode recycle gas; f10: circulating water (water); f11: water vapor; f14: a cooling medium; f15: combustion exhaust gas; and F16: auxiliary combustion of fuel; f17: auxiliary combustion of fuel; f18: and (5) assisting in burning fuel.
Detailed Description
Embodiment 1.
A fuel cell system according to embodiment 1 will be described. Fig. 1 is a system diagram showing the structure of a fuel cell system according to the present embodiment. First, the basic structure of the fuel cell system 100 according to the present embodiment will be described.
As shown in fig. 1, the fuel cell system 100 includes a fuel cell stack 1, a reformer 2, a combustor 3, a steam generator 4, a water separator 5, a recovery branch 221, an oxidizer heat exchanger 7, a water pump 8, an ejector 9, a heat recovery cooler 10, a blower 18, a raw material pretreatment device 19, a water treatment device 14, and the like. In each plant, the feedstock, oxidant, water or fluids originating from these are treated. In this embodiment, air is used as the oxidizing agent.
The fuel cell system 100 includes a control unit 90. The control unit 90 controls the entire fuel cell system 100 including the above-described devices. The control unit 90 includes a microcomputer including a CPU (Central Processing Unit ), a ROM (Read Only Memory), a RAM (Random Access Memory ), and the like.
The fuel cell system 100 includes a plurality of systems 200 to 211 and 214 to 216 each serving as a fluid flow path. Each of systems 200 to 211 and 214 to 216 is constructed using piping.
The raw material system 200 is a system that becomes a flow path of the raw material F00. The reforming raw material system 201 is a system that becomes a flow path of the raw material F01 for reforming. The fuel gas system 202 is a system that becomes a flow path of the fuel gas F02. The oxidizing agent system 203 is a system that becomes a flow path of the oxidizing agent F03. The cathode off-gas system 204 is a system that becomes a flow path of the cathode off-gas F04. The reformed gas system 205 is a system that becomes a flow path of the reformed gas F05. The anode off-gas system 206 is a system that becomes a flow path of the anode off-gas F06. The anode recycle gas system 207 is a system that serves as a flow path of the anode recycle gas F07. The recirculated combustion gas system 208 is a system that becomes a flow path of the recirculated combustion gas F08. The anode recycle gas system 209 is a system that serves as a flow path of the anode recycle gas F09. The circulating water system 210 is a system that serves as a flow path of the circulating water F10. The water vapor system 211 is a system that becomes a flow path of the water vapor F11. The heat recovery system 214 is a system that serves as a flow path of the cooling medium F14. The combustion exhaust gas system 215 is a system that becomes a flow path of the combustion exhaust gas F15. The auxiliary combustion fuel system 216 is a system that becomes a flow path of the auxiliary combustion fuel F16.
Raw material F00 such as city gas is supplied to raw material system 200 from the outside. The raw material system 200 is provided with a raw material pretreatment device 19. The raw material pretreatment device 19 is configured to remove unnecessary components such as sulfur components from the raw material F00, for example. The raw material system 200 is connected to the suction port of the ejector 9 via the reforming raw material system 201.
In this embodiment, the feed system 200 branches at its downstream end into a reformate feed system 201 and a supplementary combustion fuel system 216. The downstream end of the auxiliary combustion fuel system 216 is connected to the burner 3. Thus, a part of the raw material F00 is supplied to the burner 3 as the auxiliary combustion fuel F16 through the auxiliary combustion fuel system 216.
The ejector 9 is a circulator that circulates a fluid. The ejector 9 has an inflow port into which the driving fluid flows, a suction port into which the suction fluid flows, and an outflow port from which the mixed fluid formed by mixing the driving fluid and the suction fluid flows. Inside the ejector 9, a nozzle that ejects the driving fluid is formed. The inflow opening of the ejector 9 is connected to the water vapor system 211. The suction port of the ejector 9 is connected to the reforming raw material system 201 and the anode recycle gas system 209. The outflow opening of the injector 9 is connected to the fuel gas system 202.
The ejector 9 uses the water vapor F11 as a driving fluid and sucks at least one of the raw material F01 and the anode recycle gas F09 as a suction fluid. The suction fluid sucked by the ejector 9 flows out of the ejector 9 together with the steam F11 as the driving fluid, and is supplied to the reformer 2 through the fuel gas system 202.
The reformer 2 is configured to react steam F11 with hydrocarbons contained in the raw material F01 to generate a reformed gas F05 containing hydrogen. The reformer 2 serves as a reformer in the fuel cell system 100. The reformer 2 is thermally connected to the combustor 3 or is integrated with the combustor 3. Thereby, heat required for the reforming reaction is supplied from the burner 3 to the reformer 2. The reformer 2 is connected to the anode 1a of the fuel cell stack 1 via a reformed gas system 205.
The combustor 3 is configured to burn the cathode off-gas F04, the recirculated combustion gas F08, or the auxiliary combustion fuel F16 to generate heat. The burner 3 is connected to a combustion exhaust system 215. The gas burned by the burner 3 is discharged to the outside as the combustion exhaust gas F15 via the combustion exhaust gas system 215.
The air used as the oxidizing agent F03 is supplied to the oxidizing agent system 203 from the outside. In the oxidizer system 203, a blower 18 is provided. The blower 18 is a fluid machine for pressing the oxidizing agent F03. In the oxidizer system 203, an oxidizer heat exchanger 7 is provided. The downstream end of the oxidant system 203 is connected to the cathode 1c of the fuel cell stack 1.
The oxidizer heat exchanger 7 is thermally connected to the combustor 3 or the reformer 2. The oxidizing agent F03 passing through the oxidizing agent heat exchanger 7 is heated by heat supplied from the combustor 3 or the reformer 2. Thereby, the temperature of the oxidizing agent F03 supplied to the fuel cell stack 1 increases.
The fuel cell stack 1 is a power generation device in which a plurality of fuel cell units are stacked. The fuel cell stack 1 includes an anode 1a serving as a negative electrode, a cathode 1c serving as a positive electrode, and an electrolyte 1e. The anode 1a and the cathode 1c are separated by an electrolyte 1e. In the fuel cell stack 1, an electrochemical device composed of an anode 1a, a cathode 1c, and an electrolyte 1e is embedded using a cell member such as a flow path or a separator. The fuel cell stack 1 is configured to generate electric energy by an electrochemical reaction of the reformed gas F05 supplied to the anode 1a and the oxidizing agent F03 supplied to the cathode 1 c.
An outlet to the anode 1a is connected to the upstream end of the anode exhaust system 206. The anode exhaust system 206 is via the anode exhaust flow path 302 of the vapor generator 4. The anode off-gas system 206 is provided with the heat recovery cooler 10 downstream of the anode off-gas flow path 302. The downstream end of the anode exhaust gas system 206 is connected to the inflow port of the water separator 5.
The outlet to the cathode 1c is connected to the upstream end of the cathode exhaust system 204. The downstream end of the cathode exhaust system 204 is connected to the burner 3.
In the circulating water system 210, circulating water F10 circulates. The circulating water F10 is recovered from the water separator 5 by a water pump 8. The circulating water system 210 is provided with a water treatment device 14. The water treatment apparatus 14 is configured to remove unnecessary components such as ion components from the circulating water F10. In the fuel cell system 100, the water is substantially independent, but raw water may be added from the outside as needed.
The circulating water system 210 is provided with a water pump 8 downstream of the water treatment device 14. The water pump 8 is a fluid machine for pumping the circulating water F10. The downstream end of the circulating water system 210 is connected to one end of the evaporation flow path 301 of the vapor generator 4. An upstream end of the water vapor system 211 is connected to the other end of the evaporation flow path 301. The downstream end of steam system 211 is connected to the inflow of ejector 9.
The steam generator 4 is configured to generate steam by heating and vaporizing water. The steam generator 4 has an evaporation flow path 301, an anode off-gas flow path 302, and an auxiliary heating device 303. In the evaporation flow path 301, the circulating water F10 and the water vapor F11 obtained by vaporizing the circulating water F10 circulate. In the anode off-gas flow path 302, the anode off-gas F06 flows. The anode off-gas flow path 302 is thermally connected to the evaporation flow path 301. The auxiliary heating device 303 is configured to heat the circulating water F10 flowing through the evaporation flow path 301.
The circulating water F10 flowing into the evaporation flow path 301 is heated by heat exchange with the anode off-gas F06 flowing through the anode off-gas flow path 302. The circulating water F10 is also heated by an auxiliary heating device 303 provided independently of the anode off-gas flow path 302. The heated circulating water F10 evaporates to form water vapor F11, which flows out from the evaporation flow path 301 to the water vapor system 211. The detailed structure of the steam generator 4 will be described later with reference to fig. 2.
The heat recovery cooler 10 is a heat exchanger that performs heat exchange between the anode off-gas F06 flowing out from the anode off-gas flow path 302 of the steam generator 4 and the cooling medium F14 flowing through the heat recovery system 214.
The water separator 5 is a gas-liquid separator that separates the anode off-gas F06 into a gas component and a liquid component. The liquid outlet of the water separator 5 is connected to the circulating water system 210 upstream of the water treatment device 14 via the water pipe 6. The gas outflow port of the water separator 5 is connected to the upstream end of the anode recycle gas system 207.
The anode recycle gas system 207 branches into a recycle combustion gas system 208 and an anode recycle gas system 209 in a recycle branching 221. The downstream end of the anode recycle gas system 209 is connected to the suction port of the ejector 9.
In the recirculated combustion gas system 208, a recirculated combustion gas flow meter 312 and a recirculated combustion gas flow rate adjustment valve 311 are provided. The recirculated combustion gas flow meter 312 is configured to detect the flow rate of the recirculated combustion gas F08 flowing through the recirculated combustion gas system 208. The recirculated combustion gas flow rate adjustment valve 311 is configured to adjust the flow rate of the recirculated combustion gas F08. The recirculated combustion gas flow rate adjustment valve 311 also functions as a shut-off section that shuts off the recirculated combustion gas F08. The downstream end of the recirculated combustion gas system 208 is connected to the combustor 3.
Next, the operation of the fuel cell system 100 according to the present embodiment in the basic configuration described above will be described. The operation described below is basically the operation when the fuel cell system 100 is in the rated operation state.
In the oxidizer system 203, the oxidizer F03 flows through the blower 18. The oxidant F03 is heated in the oxidant heat exchanger 7 to a temperature suitable for the operation of the fuel cell stack 1, and is supplied to the cathode 1c of the fuel cell stack 1.
The oxidizing agent F03 supplied to the cathode 1c consumes a part of oxygen through an electrochemical reaction in a state of being separated from the reformed gas F05 by the electrolyte 1 e. The oxidizing agent F03 after consuming a part of the oxygen flows out of the cathode 1c as a cathode off-gas F04. The cathode off-gas F04 is supplied to the burner 3 through the cathode off-gas system 204.
In the raw material system 200, a raw material F00 such as city gas is circulated. Unwanted components contained in the raw material F00 are removed by the raw material pretreatment device 19. The raw material F00 after passing through the raw material pretreatment device 19 is sucked to the ejector 9 as a raw material F01 for reforming. The raw material F01 sucked to the injector 9 is mixed with the anode recycle gas F09 and the water vapor F11, and flows out of the injector 9 as the fuel gas F02. The fuel gas F02 is supplied to the reformer 2 through the fuel gas system 202. A part of the raw material F00 after passing through the raw material pretreatment device 19 passes through the auxiliary combustion fuel system 216 and is supplied to the burner 3 as the auxiliary combustion fuel F16.
The fuel gas F02 supplied to the reformer 2 is reformed in the reformer 2 to become a reformed gas F05 containing hydrogen as a main component. The reformed gas F05 flowing out of the reformer 2 is supplied to the anode 1a of the fuel cell stack 1 through the reformed gas system 205.
The reformed gas F05 supplied to the anode 1a consumes a part of the fuel by the electrochemical reaction in a state of being separated from the oxidant F03 by the electrolyte 1 e. The reformed gas F05 after consuming a part of the fuel is discharged from the anode 1a as an anode off-gas F06. The anode off-gas F06 passes through the anode off-gas system 206 and flows into the anode off-gas flow path 302 of the steam generator 4.
In the steam generator 4, heat exchange between the anode off-gas F06 and the circulating water F10 is performed. Thereby, the anode off-gas F06 is cooled, and the circulating water F10 is heated and gasified, thereby generating the water vapor F11.
The anode off-gas F06 flowing out of the vapor generator 4 flows into the heat recovery cooler 10. In the heat recovery cooler 10, heat exchange between the anode off-gas F06 and the cooling medium F14 flowing through the heat recovery system 214 is performed. Thereby, the anode off-gas F06 is further cooled. The cooled anode off-gas F06 flows into the water separator 5.
In the water separator 5, the anode off-gas F06 is separated into a gas component and a liquid component. The gas component flows out from the water separator 5 as anode recycle gas F07 to the anode recycle gas system 207. A part of the anode recycle gas F07 is supplied to the combustor 3 as a recycle combustion gas F08 through the recycle combustion gas system 208. The other anode recycle gas F07 is drawn to the ejector 9 as an anode recycle gas F09 through the anode recycle gas system 209. The anode recycle gas F09 sucked to the ejector 9 is mixed with the raw material F01 and the steam F11, and is supplied as the fuel gas F02 to the reformer 2. On the other hand, the condensed water as a liquid component flows out of the water separator 5 and is supplied to the circulating water system 210 through the water pipe 6.
In the circulating water system 210, the circulating water F10 recovered from the water separator 5 by the water pump 8 flows. Unwanted components contained in the circulating water F10 are removed by the water treatment apparatus 14. The circulating water F10 passing through the water treatment device 14 in the circulating water system 210 is supplied to the evaporation flow path 301 of the steam generator 4. In the fuel cell system 100, the water is substantially independent, but raw water may be added from the outside as needed.
In the steam generator 4, the circulating water F10 is heated by heat exchange with the anode off-gas F06 or the auxiliary heating device 303. The heated circulating water F10 evaporates to form steam F11, which flows out of the steam generator 4.
The water vapor F11 flowing out of the vapor generator 4 flows into the ejector 9 through the water vapor system 211. The water vapor F11 flowing into the ejector 9 is ejected as a driving fluid from a nozzle provided inside the ejector 9. The momentum of the ejected water vapor F11 is given to the raw material F01 and the anode recycle gas F09. Thus, the raw material F01 and the anode recycle gas F09 are mixed with the steam F11 to become the fuel gas F02, which flows out from the injector 9. The fuel gas F02 flowing out of the injector 9 is supplied to the reformer 2.
As the raw material pretreatment device 19, a filter, a desulfurizer, or the like is used. As the raw material F00, a gas containing hydrocarbon is used. Examples of the hydrocarbon-containing gas include methane gas, propane gas, butane gas, natural gas, city gas, and digested gas containing methane gas as a main component. As the raw material F00, various alcohols, petroleum-based raw materials, and the like can also be used. In the case where the raw material F00 is a hydrophilic liquid raw material, the raw material F00 may be mixed in advance with the circulating water. On the other hand, in the case where the raw material F00 is a hydrophobic liquid raw material, the raw material F00 monomer may be preheated and gasified, or the raw material F00 and the water vapor F11 may be mixed and preheated and gasified.
In the reformer 2, for example, a steam reforming reaction is performed. A typical reforming reaction using methane as a raw material is represented by the formula (1) and the formula (2). Inside the reformer 2, a reforming catalyst is filled. The endothermic reaction of methane and steam is caused by the reforming catalyst. By this reaction, hydrogen is generated. In general, the flow rate of the steam supplied to the reformer 2 is expressed by the value of S/C. S/C is the mole fraction of water vapor (S) relative to carbon (C) contained in the fuel gas. In general, the flow rate of the steam to be supplied to the reformer 2 is set so that the value of S/C becomes a constant value in the range of 2.5 to 3.5. Reforming catalysts, e.g. having a catalyst in Al 2 O 3 The support such as MgO carries thereon a catalyst such as Ni-based catalyst, pt-based catalyst, ru-based catalyst, or the like.
In addition, the steam reforming reaction is exemplified here, but the reforming reaction is not limited thereto. As the reforming reaction, an autothermal reforming reaction or a partial oxidation reforming reaction in which air is additionally introduced into the reformer 2 may be used.
The fuel cell stack 1 generates an electrochemical reaction between the reformed gas F05 supplied to the anode 1a and the oxidizing agent F03 supplied to the cathode 1c in a state where the reformed gas and the oxidizing agent F03 are separated from each other by the electrolyte 1 e. Thereby, in the fuel cell stack 1, exchange of electrons is caused, thereby generating electric energy. Specifically, a potential difference is generated in the fuel cell stack 1, and at the same time, ion transfer via the electrolyte 1e and electron transfer in the circuit via the output terminals of both the anode 1a and the cathode 1c are generated. At this time, a direct current generated by movement of electrons in the circuit is outputted as electric power.
The electrode material, operating temperature, etc. of the fuel cell stack 1 are different depending on the kind of the electrolyte 1 e. The type of ions moving in the electrolyte 1e also varies depending on the type of the electrolyte 1 e. For example, in the case of a solid oxide fuel cell, the electrode reaction in the anode 1a is represented by formula (3), and the electrode reaction in the cathode 1c is represented by formula (4).
H 2 +O 2- →H 2 O+2e - …(3)
1/2O 2 +2e - →O 2- …(4)
In the anode 1a, hydrogen corresponding to the movement amount of electrons is consumed by the electrode reaction. Thus, in the anode 1a, the closer to the anode outlet, the lower the hydrogen partial pressure becomes. In addition, in the anode 1a, water having the same mass as that of the consumed hydrogen is generated. Therefore, in the anode 1a, the closer to the anode outlet, the higher the water vapor partial pressure becomes.
On the other hand, in the cathode 1c, oxygen corresponding to the amount of movement of electrons is consumed by the electrode reaction. Thus, in the cathode 1c, the closer to the cathode outlet, the smaller the gas flow rate becomes and the lower the oxygen partial pressure becomes. In the case of a solid oxide fuel cell, internal reforming in which the electrode reaction and the reforming reaction are simultaneously performed can be realized in the anode 1 a. In this case, in the anode 1a, the reforming reaction of the surplus methane that cannot be reformed in the reformer 2 can be performed in the direction of generating hydrogen.
The fuel cell stack 1 is often operated such that the ratio of the amount of hydrogen consumed in the electrode reaction of the anode 1a to the flow rate of hydrogen supplied from the reformer 2 or generated by internal reforming is 0.60 to 0.85. That is, the remaining fuel is contained in the anode off-gas F06 at the anode outlet. For example, the volume mole fraction of hydrogen contained in the anode off-gas F06 at the anode outlet is about 12%. In addition, for example, the volume mole fraction of water vapor contained in the anode off-gas F06 at the anode outlet is about 60%.
In addition, the fuel cell stack 1 is often operated such that the ratio of the amount of oxygen consumed in the electrode reaction of the cathode 1c to the amount of oxygen supplied via the oxidizing agent system 203 is 0.15 to 0.50. That is, the cathode off-gas F04 at the cathode outlet contains the remaining oxygen. For example, the volume mole fraction of oxygen contained in the cathode off-gas F04 at the cathode outlet is about 16%.
The detailed structure of the fuel cell system 100 according to the present embodiment will be described based on the basic structure and operation of the fuel cell system 100 described above.
In the fuel cell system 100 according to the present embodiment, the temperature difference between the anode off-gas F06 and the circulating water F10, the enthalpy difference, and the auxiliary heating device 303 are used as heat sources of the vapor generator 4. This point is also the same as in the fuel cell system 100 according to embodiment 2 and the following.
Fig. 2 is a cross-sectional view showing an internal structure of the vapor generator of the fuel cell system according to the present embodiment. The vertical direction in fig. 2 is a vertical direction. The thick arrows in fig. 2 indicate the flow direction of the fluid.
As shown in fig. 2, the steam generator 4 has a cylindrical shape as a whole. The central axis 4a of the vapor generator 4 is along the up-down direction. The steam generator 4 has an outer peripheral wall 4b and an inner peripheral wall 4c provided on the inner peripheral side of the outer peripheral wall 4 b. The outer peripheral wall 4b and the inner peripheral wall 4c are each formed in a cylindrical shape centered on the central axis 4a, and extend in the vertical direction. An annular space is formed between the outer peripheral wall 4b and the inner peripheral wall 4c.
A partition wall 4d is formed between the outer peripheral wall 4b and the inner peripheral wall 4c, that is, on the inner peripheral side of the outer peripheral wall 4b and on the outer peripheral side of the inner peripheral wall 4 c. The partition wall 4d is formed in a cylindrical shape coaxially with the outer peripheral wall 4b and the inner peripheral wall 4c, and extends in the up-down direction. The space formed between the outer peripheral wall 4b and the inner peripheral wall 4c is partitioned into an outer peripheral space 41 and an inner peripheral space 42 by a partition wall 4d. The outer peripheral space 41 and the inner peripheral space 42 are annular spaces. The upper end of the outer peripheral space 41 and the upper end of the inner peripheral space 42 are closed by the upper wall 4 e. The lower end of the outer peripheral space 41 and the lower end of the inner peripheral space 42 are closed by the lower wall 4 f. The upper wall 4e and the lower wall 4f are formed in a circular ring shape.
The evaporation flow path 301 is provided in the inner peripheral space 42. A heat transfer tube 301a having a spiral tube structure is formed in the inner peripheral space 42. The heat transfer pipe 301a extends spirally along the partition wall 4d with the central axis 4a as a spiral axis. An evaporation flow path inlet 301b serving as an inlet of the evaporation flow path 301 is provided at an upper end portion of the heat transfer pipe 301a. An evaporation channel outlet 301c, which is an outlet of the evaporation channel 301, is provided at a lower end portion of the heat transfer tube 301a. The heat transfer pipe 301a is provided so that the height from the lower wall 4f toward the evaporation flow path outlet 301c from the evaporation flow path inlet 301b becomes monotonically low. The heat transfer tube 301a is closely adhered to the inner peripheral surface of the partition wall 4d. Thereby, the heat energy is easily moved between the heat transfer pipe 301a and the partition wall 4d.
The evaporation flow path 301 is formed inside the heat transfer tube 301 a. That is, the evaporation flow path 301 is formed in a spiral shape having the central axis 4a as a spiral axis. The evaporation flow path 301 extends obliquely to the up-down direction. In the evaporation flow path 301, a downward slope is generated from the upstream side toward the downstream side. The circulating water F10 flowing into the evaporation channel 301 from the evaporation channel inlet 301b gradually evaporates while flowing downward along the evaporation channel 301, and flows out as water vapor F11 from the evaporation channel outlet 301 c.
The auxiliary heating device 303 is a heating device that heats the circulating water F10 flowing through the evaporation flow path 301. The auxiliary heating device 303 is provided in the inner peripheral space 42. The auxiliary heating device 303 is provided on the inner peripheral side of the evaporation channel 301, that is, between the evaporation channel 301 and the center axis 4 a. The auxiliary heating device 303 is controlled by the control unit 90.
As the auxiliary heating device 303, an electric heater or the like is used. For example, the auxiliary heating device 303 has a plurality of electric heaters each formed in a straight pipe shape. In this case, the plurality of electric heaters are arranged on a circumference centered on the central axis 4 a. The plurality of electric heaters are each arranged parallel to the central axis 4 a. The auxiliary heating device 303 may be formed in a cylindrical shape centering on the central axis 4 a.
The inner peripheral space 42 is filled with a heat transfer promoting member 306 around the evaporation flow path 301 and the auxiliary heating device 303. Thereby, the heat energy is easily moved between the evaporation flow path 301 and the auxiliary heating device 303. The evaporation flow path 301 and the auxiliary heating device 303 are thermally connected to each other via a heat transfer promoting member 306. As the heat transfer promoting member 306, for example, metal particles, metal mesh, heat transfer cement, or the like is used.
The anode off-gas flow passage 302 is provided in the outer peripheral space 41. In the present embodiment, the entire outer peripheral space 41 serves as the anode off-gas flow path 302. The anode off-gas flow path 302 is defined by an outer peripheral wall 4b, a partition wall 4d, an upper wall 4e, and a lower wall 4 f. That is, the outer peripheral wall 4b, the partition wall 4d, the upper wall 4e, and the lower wall 4f serve as flow path walls of the anode off-gas flow path 302.
The anode off-gas flow path 302 is thermally connected to the evaporation flow path 301 via the partition wall 4d and the heat transfer pipe 301 a. The anode off-gas flow field 302 is provided with heat transfer fins, for example, offset fins, which are thermally connected to the partition wall 4 d. This improves the heat transfer performance between the anode off-gas F06 and the partition wall 4d, and thus can achieve downsizing of the vapor generator 4.
The steam generator 4 has an inflow pipe 307a forming an anode off-gas flow path inlet 307 and an outflow pipe 308a forming an anode off-gas flow path outlet 308. The anode off-gas F06 flows into the anode off-gas flow path 302 via the inflow pipe 307a, and flows out of the anode off-gas flow path 302 via the outflow pipe 308a.
The inflow pipe 307a is connected to a lower portion of the anode off-gas flow path 302. The inflow pipe 307a penetrates the outer peripheral wall 4b and extends in the radial direction of the steam generator 4. Here, the radial direction of the vapor generator 4 is a direction along the radius of the vapor generator 4 centered on the central axis 4 a.
The outflow pipe 308a is connected to an upper end portion of the anode off-gas flow passage 302. The outflow pipe 308a penetrates the outer peripheral wall 4b and extends in the radial direction of the vapor generator 4. The outflow pipe 308a is disposed at a position symmetrical to the inflow pipe 307a about the central axis 4a when viewed along the central axis 4 a.
The anode off-gas F06 flows through the anode off-gas flow field 302 from the anode off-gas flow field inlet 307 toward the anode off-gas flow field outlet 308. The circulating water F10 and the water vapor F11 flow from top to bottom, whereas the anode off-gas F06 flows from bottom to top. That is, the flow of the anode off-gas F06 is counter-current to the flow of the circulating water F10 and the water vapor F11.
Heat exchange between the anode off-gas F06 and the circulating water F10 is performed between the anode off-gas flow path 302 and the evaporation flow path 301. Thereby, the circulating water F10 is heated and gasified, and steam F11 is generated.
The anode off-gas flow path 302 and the auxiliary heater 303 are opposed to each other across the evaporation flow path 301. That is, the evaporation flow path 301 is sandwiched between the anode off-gas flow path 302 and the auxiliary heating device 303. Thus, the circulating water F10 flowing through the evaporation flow path 301 is heated from both sides by the anode off-gas F06 and the auxiliary heating device 303.
The anode off-gas flow path 302 is provided with a dew condensation water depositing space 304 for depositing dew condensation water below both the inflow pipe 307a and the outflow pipe 308 a. That is, the dew condensation water depositing space 304 is provided below both the anode off-gas flow path inlet 307 and the anode off-gas flow path outlet 308. A dew condensation water discharging tube 305 is connected to the bottom of the dew condensation water depositing space 304. The dew water discharging tube 305 extends downward through the lower wall 4 f. The dew condensation water discharging tube 305 is provided with a dew condensation water discharging valve 305a.
The water vapor system 211 located downstream of the evaporation flow path 301 is provided with a water vapor temperature sensor 20. The steam temperature sensor 20 is configured to detect the temperature of the steam F11 flowing out of the evaporation flow path 301, and output a detection signal to the control unit 90.
The anode off-gas system 206 is provided with an anode off-gas temperature sensor 21 on the downstream side of the anode off-gas flow path 302. The anode off-gas temperature sensor 21 is configured to detect the temperature of the anode off-gas F06 flowing out of the anode off-gas flow path 302, and output a detection signal to the control unit 90.
Next, the operation of the fuel cell system 100, which is mainly configured as described above, will be described. The circulating water F10 is supplied to the evaporation passage 301 of the steam generator 4 by the water pump 8. The circulating water F10 flows through the evaporation channel 301 from the evaporation channel inlet 301b toward the evaporation channel outlet 301c by the discharge pressure of the water pump 8 and gravity.
The anode off-gas F06 discharged from the anode 1a is supplied to the anode off-gas flow path 302 of the steam generator 4. Heat energy is transferred from the anode off-gas F06 flowing through the anode off-gas flow path 302 to the circulating water F10 flowing through the evaporation flow path 301 via the partition wall 4d and the heat transfer pipe 301 a. Thereby, the circulating water F10 is gasified to form steam F11. The anode off-gas F06 flowing out of the anode off-gas flow path 302 flows into the heat recovery cooler 10 through the anode off-gas system 206.
The control unit 90 obtains information on the temperature of the anode off-gas F06 flowing out of the anode off-gas flow path 302 based on the detection signal from the anode off-gas temperature sensor 21. The control unit 90 controls the auxiliary heating device 303 based on the temperature of the anode off-gas F06 flowing out of the anode off-gas flow path 302. Specifically, the control unit 90 operates the auxiliary heating device 303 when the temperature of the anode off-gas F06 detected by the anode off-gas temperature sensor 21 is lower than the lower threshold value. The control unit 90 stops the auxiliary heating device 303 when the temperature of the anode off-gas F06 detected by the anode off-gas temperature sensor 21 exceeds an upper threshold.
The control of the auxiliary heating means 303 may be either on-off control or phase or continuous phase control. For example, when the temperature of the anode off gas F06 detected by the anode off gas temperature sensor 21 is between the lower limit threshold value and the upper limit threshold value, the control unit 90 may control the output of the auxiliary heating device 303 in accordance with the temperature stage or continuously.
When the auxiliary heating device 303 is operated, the circulating water F10 flowing through the evaporation flow path 301 is heated by the anode off-gas F06, and is also heated by the auxiliary heating device 303. That is, the circulating water F10 flowing through the evaporation flow path 301 is heated from both sides by the anode off-gas F06 flowing through the anode off-gas flow path 302 and the auxiliary heating device 303. Thereby, sufficient vaporization heat is provided to the circulating water F10.
The anode off-gas temperature sensor 21 may be provided at or near the anode off-gas flow path outlet 308. Even in this case, the control unit 90 controls the auxiliary heating device 303 in the same manner as described above, based on the temperature of the anode off-gas F06 detected by the anode off-gas temperature sensor 21.
In the present embodiment, the auxiliary heating device 303 is controlled in accordance with the temperature of the anode off-gas F06 flowing out of the anode off-gas flow path 302, but the control of the auxiliary heating device 303 is not limited to this. The control unit 90 may control the auxiliary heating device 303 based on the detected temperature of the steam temperature sensor 20, that is, the temperature of the steam F11 flowing out of the evaporation flow path 301. The control unit 90 may control the auxiliary heating device 303 based on both the temperature of the anode off-gas F06 flowing out of the anode off-gas flow path 302 and the temperature of the water vapor F11 flowing out of the evaporation flow path 301.
The anode off-gas temperature sensor 21 may be provided upstream of the anode off-gas flow path 302 in the anode off-gas system 206. In this case, the control unit 90 calculates the heat energy of the anode off-gas F06 based on the detection signal of the anode off-gas temperature sensor 21 and the operation condition signal of the fuel cell system 100 input to the control unit 90. The control unit 90 compares the heat energy of the anode off-gas F06 with the heat energy required for the vaporization of the circulating water F10, and controls the output of the auxiliary heating device 303 based on the deviation when the heat energy required for the vaporization of the circulating water F10 is insufficient.
In the fuel cell system 100, the control unit 90 does not need to operate the auxiliary heating device 303 when the heat energy required for the vaporization of the circulating water F10 can be obtained from the anode off-gas F06. On the other hand, when the heat energy required for the vaporization of the circulating water F10 is not obtained from the anode off-gas F06 due to fluctuation in the output of the fuel cell system 100 or the like, the control unit 90 operates the auxiliary heating device 303.
In the anode off-gas flow path 302, when the temperature of the anode off-gas F06 falls below the dew point due to the heat energy imparted from the anode off-gas F06 to the circulating water F10, dew condensation occurs in the anode off-gas F06. In the present embodiment, dew condensation water generated by dew condensation of the anode off-gas F06 is accumulated in the dew condensation water accumulating space 304 provided below the anode off-gas flow passage inlet 307. The dew-point water accumulated in the dew-point water depositing space 304 is appropriately discharged through the dew-point water discharging valve 305 a. This can suppress clogging of the anode off-gas flow path 302 with dew condensation water, and therefore can suppress generation of pulsation in the anode off-gas F06.
It is preferable that the dew condensation water is automatically discharged according to the amount of dew condensation water in the dew condensation water storing space 304. For example, the dew-water drainage valve 305a may be configured to be opened by the weight of dew-water inside the dew-water storing space 304. Alternatively, a U-pipe may be provided in the dew condensation water discharging pipe 305 so that dew condensation water is discharged according to a head difference of dew condensation water. Of course, the dew-water discharging valve 305a may be opened and closed by a timer to periodically discharge dew-water.
The anode off-gas F06 flowing out of the anode off-gas flow path 302 further supplies heat energy to the cooling medium F14 in the heat recovery cooler 10, and flows into the water separator 5. The temperature of the anode off-gas F06 flowing into the water separator 5 becomes a predetermined temperature equal to or lower than the dew point. In order to bring the temperature of the anode off-gas F06 in the water separator 5 close to the target temperature, the control unit 90 controls the flow rate of the cooling medium F14 based on the temperature of the anode off-gas F06 after passing through the heat recovery cooler 10 or the temperature of the anode off-gas F06 in the water separator 5. The temperature of the anode off-gas F06 after passing through the heat recovery cooler 10 or the temperature of the anode off-gas F06 in the water separator 5 is detected by a temperature sensor, not shown.
In the water separator 5, the moisture contained in the anode off-gas F06 liquefies according to the saturated vapor pressure at the temperature of the anode off-gas F06. The liquefied water is separated from the anode off-gas F06 as water droplets, and is stored as condensed water in the lower portion of the water separator 5. The condensed water accumulated in the water separator 5 is supplied to the circulating water system 210 as the circulating water F10 through the water pipe 6. The circulating water F10 is supplied to the steam generator 4 by the water pump 8 according to the flow rate of the steam F11 required for the fuel gas F02.
On the other hand, the anode off-gas F06 from which the water content has been removed by the water separator 5 flows out of the water separator 5 as the anode recycle gas F07, passes through the anode recycle gas system 207, and reaches the recycle branching portion 221. The anode recycle gas F07 is divided into a recycle combustion gas F08 flowing through the recycle combustion gas system 208 and an anode recycle gas F09 flowing through the anode recycle gas system 209 in the recycle branching portion 221. The recirculated combustion gas F08 is supplied to the combustor 3 through the recirculated combustion gas flow meter 312 and the recirculated combustion gas flow rate adjustment valve 311.
For example, the opening degree of the recirculated combustion gas flow rate adjustment valve 311 is controlled by the control unit 90 based on a flow rate signal from the recirculated combustion gas flow meter 312. Thus, the recycle branch portion 221 distributes the recirculated combustion gas F08 and the anode recycle gas F09 at an appropriate flow rate ratio according to the operating conditions of the fuel cell system 100. Therefore, the fuel cell system 100 is highly efficient.
The combustor 3 is supplied with the recirculated combustion gas F08, the cathode off-gas F04 discharged from the cathode 1c, and the auxiliary combustion fuel F16. In the burner 3, these gases are burned. A part of the heat energy of the burned gas is supplied to the reformer 2 as the heat energy required for the reforming reaction. Thereby, the temperature of the reformer 2 is raised to a temperature required for the reforming reaction. The temperature required for the reforming reaction in the reformer 2 is 600 ℃, for example.
Another part of the heat energy of the burned gas is supplied to the oxidizing agent F03 in the oxidizing agent heat exchanger 7. Thereby, the temperature of the oxidizing agent F03 increases to a temperature at which the cathode 1c of the fuel cell stack 1 can operate. For example, the temperature of the oxidizing agent F03 is increased from 25 ℃ which is the temperature of the outside air to 600 ℃.
After the heat energy is supplied to the reformer 2 and the oxidizer heat exchanger 7, the gas burned in the combustor 3 is discharged to the outside as a combustion exhaust gas F15 through the combustion exhaust gas system 215.
The anode recycle gas F09 is drawn to the ejector 9 through the anode recycle gas system 209. The anode circulation gas F09 sucked to the injector 9 is mixed with the water vapor F11 and the raw material F01, and flows out of the injector 9 as the fuel gas F02. The fuel gas F02 is supplied to the reformer 2 through the fuel gas system 202.
Based on the enthalpy of each output of the fuel cell stack 1, whether or not the above-described operation is established is studied. As an example, the fuel cell system 100 includes a solid oxide fuel cell using city gas as a raw material, and is configured to operate with a fuel utilization rate of 75%, a cell voltage of 0.84V, and a current of 24A. Under this condition, the enthalpy per output of the fuel cell stack 1 in the anode off-gas F06 at the anode outlet becomes-3081J/s·kw.
On the other hand, the vaporization heat required for converting the circulating water F10 into the steam F11 was estimated to be 247J/s.kW. Thereby, the temperature of the anode off-gas F06 after the heat energy is supplied to the circulating water F10 in the steam generator 4 exceeds 150 ℃ calculated from the heat balance. That is, the heat energy required for converting the circulating water F10 into the water vapor F11 in the vapor generator 4 can be supplied by heat exchange between the circulating water F10 and the anode off-gas F06.
The temperature of the anode off-gas F06 in the water separator 5 is set to 60 ℃. The saturated vapor pressure at this temperature was about 0.025MPa. The volume mole fraction of water vapor contained in the anode off-gas F06 at the anode outlet is about 60%. In contrast, the volume mole fraction of the water vapor contained in the anode off-gas F06 in the water separator 5 decreases to about 20% as the flow rate of the water vapor decreases to 1/2 due to condensation of the water vapor. The anode off-gas F06 flows out of the water separator 5 as an anode recycle gas F07.
The anode recycle gas F07 flowing out of the water separator 5 is distributed into the recycle combustion gas F08 and the anode recycle gas F09 at the respective flow rates of approximately the same level in the recycle branching portion 221.
Therefore, the flow rate of the anode recycle gas F09 becomes about 1/4 of the flow rate of the anode off-gas F06 at the anode outlet. The flow rate of the water vapor contained in the anode recycle gas F09 is about 8% of the flow rate of the water vapor contained in the anode off-gas F06 at the anode outlet. The flow rate of the water vapor contained in the anode off-gas F06 at the anode outlet is only 15% to the flow rate of the water vapor required for the reformer 2 or the fuel cell stack 1. In order to supplement the insufficient amount of water vapor, the circulating water F10 is gasified in the vapor generator 4 to generate water vapor F11 of about 0.5 MPa.
Next, the operation of the fuel cell system 100 in the case where the output of the fuel cell stack 1 is increased will be described. When the output of the fuel cell stack 1 increases, the flow rates of the oxidant F03, the raw material F01, and the steam F11, which are gases required for the cell reaction, increase according to the output load conditions by the control of the control unit 90.
At this time, when the value of S/C in the reforming catalyst filling section in the reformer 2 is smaller than a certain value, the reforming reaction represented by the formulas (1) and (2) may not be caused, and carbon (C) may be deposited. As a result, the deposited C may cause problems such as flow path blocking. In order to avoid this problem, the control unit 90 increases the flow rate of the steam F11 earlier than the flow rate of the raw material F01. That is, when the output of the fuel cell stack 1 is increased, first, the flow rate of the water vapor F11, that is, the flow rate of the circulating water F10 needs to be increased. Concomitantly, the steam generator 4 requires vaporization heat corresponding to the flow rate increase of the circulating water F10.
In the present embodiment, when the flow rate of the circulating water F10 increases, the temperature of the anode off-gas F06 detected by the anode off-gas temperature sensor 21 decreases, so the auxiliary heating device 303 operates. That is, the auxiliary heating device 303 supplies heat energy to the circulating water F10 in the evaporation flow path 301 in an auxiliary manner. Thereby, the auxiliary heating device 303 supplements the vaporization heat corresponding to the flow rate increase of the circulating water F10.
After the completion of the transition of the operation state of the fuel cell system 100 accompanied by an increase in the output of the fuel cell stack 1, the heat energy from the anode off-gas F06 can be used to supply the heat of vaporization of the circulating water F10. In this case, the temperature of the anode off-gas F06 detected by the anode off-gas temperature sensor 21 rises, so the auxiliary heating device 303 stops. After the auxiliary heating device 303 is stopped, the circulating water F10 flowing through the evaporation flow path 301 is heated from the one-side only by the anode off-gas F06 flowing through the anode off-gas flow path 302.
As described above, according to the present embodiment, water vapor can be stably supplied according to the operating state of the fuel cell system 100.
The operation of the fuel cell system 100 in the case where the output of the fuel cell stack 1 is increased is not limited to the above example. In the case where the vaporization heat of the circulating water F10 is insufficient due to the operation condition of the fuel cell system 100, the auxiliary heating device 303 may be operated continuously or intermittently. In addition, in the case where the increase in the output of the fuel cell stack 1 is small and the increase in the vaporization heat of the circulating water F10 can be supplied by the heat energy from the anode off-gas F06, the auxiliary heating 303 may not be operated.
In the present embodiment, the circulating water F10 can be converted into the steam F11 by using the heat energy of the anode off-gas F06 flowing through the anode off-gas system 206. Therefore, the flow rate of the recirculated combustion gas F08 supplied to the combustor 3 can be reduced, and the flow rate of the anode recycle gas F09 returned to the reformer 2 via the ejector 9 can be increased. Therefore, according to the present embodiment, the fuel cell system 100 with high energy efficiency can be realized.
In the present embodiment, in the steam generator 4, the anode off-gas flow path 302 and the auxiliary heating device 303 face each other across the evaporation flow path 301. Therefore, the circulating water F10 flowing through the evaporation flow path 301 can be heated from both sides. Therefore, according to the present embodiment, heat loss can be reduced, and therefore, the fuel cell system 100 that can obtain higher energy efficiency can be realized.
Further, in the present embodiment, it is possible to supply water vapor with high responsiveness and stability according to the operating conditions of the fuel cell system 100. Therefore, according to the present embodiment, the fuel cell system 100 can be miniaturized.
In the present embodiment, even if the anode off-gas F06 is condensed in the anode off-gas flow path 302 due to the transient operation state of the fuel cell system 100, dew condensation water can be accumulated in the dew condensation water accumulating space 304. This can prevent the flow of the anode off-gas F06 from being hindered by dew condensation water, and therefore can suppress pulsation from occurring in the anode off-gas F06.
In the present embodiment, the circulating water F10 can be turned into the water vapor F11 using the waste heat of the anode off-gas F06. Therefore, according to the present embodiment, the heat energy of the fuel cell system 100 can be effectively utilized, so that the fuel cell system 100 with high energy efficiency can be realized.
In the transient operation state of the fuel cell system 100, the heat energy that can be obtained from the anode off-gas F06 may be insufficient with respect to the heat energy required as the vaporization heat of the circulating water F10. In this embodiment, even in such a case, the auxiliary heating device 303 can supplement the heat energy with good responsiveness. Therefore, in the present embodiment, a wide range of operating conditions of the fuel cell system 100 can be handled.
In the present embodiment, the auxiliary heating device 303 can be stopped when the heat energy required for the vaporization heat of the circulating water F10 can be obtained from the anode off-gas F06. Therefore, it is not necessary to constantly supply energy to the auxiliary heating 303. Therefore, according to the present embodiment, the fuel cell system 100 with high energy efficiency can be realized.
Fig. 3 is a cross-sectional view showing the structure of an anode off-gas flow path inlet and its surroundings in the steam generator according to modification 1-1 of the present embodiment. As shown in fig. 3, the inflow pipe 307a has an end surface 307a1. The end face 307a1 faces the anode off-gas flow path 302. The end surface 307a1 is formed perpendicularly to the tube axis of the inflow tube 307 a. The end surface 307a1 is formed on a surface different from the inner wall surface 4b1 of the outer peripheral wall 4 b. In the present modification, the inflow pipe 307a is inserted into the anode off-gas flow path 302, and therefore the end surface 307a1 protrudes toward the inside of the anode off-gas flow path 302 with respect to the inner wall surface 4b 1. However, the end surface 307a1 is separated from the partition wall 4d.
The anode off-gas F06 flows into the anode off-gas flow path 302 via the inflow pipe 307a, flows upward in the anode off-gas flow path 302, and flows out of the steam generator 4. When condensation occurs in the anode off-gas F06, the condensation water mainly flows down along the inner wall surface 4b1 of the outer peripheral wall 4b, and moves to the condensation water storage space 304.
In the present modification, the end surface 307a1 of the inflow pipe 307a is formed on a surface different from the inner wall surface 4b1, so that dew condensation water flowing down along the inner wall surface 4b1 is less likely to enter the inside of the inflow pipe 307 a. Therefore, the flow of the anode off-gas F06 can be prevented from being hindered by dew condensation water, so that generation of pulsation in the anode off-gas F06 can be suppressed.
In particular, in the present modification, the end surface 307a1 of the inflow pipe 307a protrudes toward the inside of the anode off-gas flow path 302 with respect to the inner wall surface 4b1, so that the penetration of dew condensation water into the inside of the inflow pipe 307a can be prevented more reliably. Therefore, pulsation in the anode off-gas F06 can be more reliably prevented.
Fig. 4 is a cross-sectional view showing the structure of an anode off-gas flow path inlet and its surroundings in the steam generator according to modification 1-2 of the present embodiment. As shown in fig. 4, the end surface 307a1 of the inflow pipe 307a is formed inclined with respect to the pipe axis of the inflow pipe 307a, except for being formed on a surface different from the inner wall surface 4b 1. The end surface 307a1 is inclined with respect to the inner wall surface 4b1 so as to be farther from the inner wall surface 4b1 as it goes upward. Therefore, in the present modification, dew condensation water is more difficult to be immersed in the inside of the inflow pipe 307a than in the structure of modification 1-1. Therefore, according to the present modification, the flow of the anode off-gas F06 can be more reliably prevented from being hindered by dew condensation water, so that pulsation can be more reliably prevented from occurring in the anode off-gas F06.
Fig. 5 is a cross-sectional view showing the structure of an anode off-gas flow path inlet and its surroundings in the steam generator according to modification 1-3 of the present embodiment. As shown in fig. 5, in the present modification, a dew condensation water guide plate 313 is formed in the anode off-gas flow path 302 above the anode off-gas flow path inlet 307. One end 313a of the dew water guide plate 313 is joined to the inner wall surface 4b1 at a position above the anode off-gas flow path inlet 307. The dew condensation water guiding plate 313 is inclined so that the height becomes lower as it gets farther from the inner wall surface 4b1, that is, as it gets closer to the other end portion 313b of the dew condensation water guiding plate 313. A gap is formed between the other end 313b of the dew condensation water guiding plate 313 and the partition wall 4 d. The other end 313b may be joined to the partition wall 4 d. The inflow pipe 307a and the anode off-gas flow path inlet 307 of this modification have the same structure as that shown in fig. 2.
After reaching one end 313a of the dew condensation water guide plate 313, dew condensation water flowing down along an inner wall surface 4b1 of the outer peripheral wall 4b is guided to the other end 313b side by the dew condensation water guide plate 313. The dew condensation water flows toward the other end portion 313b side according to the inclination of the dew condensation water guiding plate 313, and drips downward from the other end portion 313 b. The dripped dew-point water is accumulated in the dew-point water accumulating space 304. Therefore, according to the present modification, the flow of the anode off-gas F06 can be prevented from being hindered by dew condensation water, so that pulsation can be prevented from occurring in the anode off-gas F06.
In the present modification, at least 1 through hole 313c is formed in the dew condensation water guiding plate 313. The through holes 313c each penetrate the dew-water guide plate 313 in the thickness direction of the dew-water guide plate 313. Accordingly, the through hole 313c becomes a part of the flow path of the anode off-gas F06, so that the anode off-gas F06 flowing into the anode off-gas flow path 302 easily flows upward. In addition, in the case where the flow path of the anode off-gas F06 is sufficiently ensured, the through-holes 313c may not be formed in the dew condensation water guiding plate 313.
As described above, the fuel cell system 100 according to the present embodiment includes the vapor generator 4, the reformer 2, the fuel cell stack 1, and the injector 9. The steam generator 4 is configured to heat the circulating water F10 to generate steam F11. The reformer 2 is configured to react steam F11 with hydrocarbons to generate a reformed gas F05 containing hydrogen. The fuel cell stack 1 has an anode 1a and a cathode 1c. The fuel cell stack 1 is configured to generate electric energy by an electrochemical reaction of the reformed gas F05 supplied to the anode 1a and the oxidizing agent F03 supplied to the cathode 1c. The ejector 9 is configured to supply at least one of a raw material F01 containing hydrocarbons and an anode recycle gas F09 obtained by recovering a part of the anode off-gas F06 discharged from the anode 1a to the reformer 2, using the water vapor F11 as a driving fluid. The steam generator 4 has: an evaporation flow path 301 through which the circulating water F10 flows; an anode off-gas flow path 302 thermally connected to the evaporation flow path 301, through which the anode off-gas F06 flows; and an auxiliary heating device 303 for heating the circulating water F10. The anode off-gas flow path 302 and the auxiliary heater 303 are opposed to each other across the evaporation flow path 301. Here, the reformer 2 is an example of a reformer. The circulating water F10 is an example of water.
According to this configuration, the circulating water F10 flowing through the evaporation flow path 301 can be heated from both sides by the anode off-gas flow path 302 and the auxiliary heating device 303. Therefore, according to the present embodiment, the heat loss can be reduced, and therefore, the fuel cell system 100 with higher energy efficiency can be realized.
In the fuel cell system 100 according to the present embodiment, the evaporation flow path 301 extends obliquely with respect to the vertical direction. In the evaporation flow path 301, a downward slope is generated from the upstream side toward the downstream side. According to this configuration, the circulating water F10 can flow through the evaporation flow path 301 by gravity.
In the fuel cell system 100 according to the present embodiment, the anode off-gas flow path 302 extends in the up-down direction. The steam generator 4 has an outer peripheral wall 4b, an inflow pipe 307a, and an outflow pipe 308a. The peripheral wall 4b extends in the up-down direction. The outer peripheral wall 4b defines an anode off-gas flow path 302. The inflow pipe 307a penetrates the outer peripheral wall 4b and is connected to the anode off-gas flow passage 302. The anode off-gas F06 flows in from the inflow pipe 307 a. The outflow pipe 308a is connected to the anode off-gas flow passage 302 above the inflow pipe 307 a. The anode off-gas F06 flows out from the outflow pipe 308a. The anode off-gas flow path 302 is provided with a dew condensation water depositing space 304 for depositing dew condensation water below the inflow pipe 307 a. Here, the outer peripheral wall 4b is an example of a flow path wall.
With this configuration, the anode off-gas flow path 302 can be prevented from being blocked by dew condensation water, and therefore generation of pulsation in the anode off-gas F06 can be prevented.
In the fuel cell system 100 according to the present embodiment, the inflow pipe 307a has an end surface 307a1 facing the anode off-gas flow path 302. The end surface 307a1 protrudes further toward the inside of the anode off-gas flow passage 302 than the inner wall surface 4b1 of the outer peripheral wall 4 b. With this configuration, the dew condensation water can be prevented from entering the inside of the inflow pipe 307a, and pulsation can be prevented from occurring in the anode off-gas F06.
In the fuel cell system 100 according to the present embodiment, the anode off-gas flow path 302 is provided with a dew condensation water guide plate 313 for guiding dew condensation water above the inflow pipe 307 a. With this configuration, the dew condensation water can be prevented from entering the inside of the inflow pipe 307a, and pulsation can be prevented from occurring in the anode off-gas F06.
In the fuel cell system 100 according to the present embodiment, the auxiliary heating device 303 has an electric heater. According to this structure, the output of the auxiliary heating apparatus 303 can be easily adjusted.
The fuel cell system 100 according to the present embodiment further includes an anode off-gas temperature sensor 21 that detects the temperature of the anode off-gas F06, and a control unit 90. The control unit 90 controls the auxiliary heating device 303 based on the temperature of the anode off-gas F06.
According to this structure, even when the heat energy available from the anode off-gas F06 is insufficient for the heat energy required as the vaporization heat of the circulating water F10, the heat energy can be supplemented by the auxiliary heating device 303.
The fuel cell system 100 according to the present embodiment further includes a water vapor temperature sensor 20 that detects the temperature of the water vapor F11, and a control unit 90. The control unit 90 controls the auxiliary heating device 303 based on the temperature of the water vapor F11.
According to this structure, even when the heat energy obtained from the anode off-gas F06 is insufficient for the heat energy required as the vaporization heat of the circulating water F10, the heat energy can be supplemented by the auxiliary heating device 303.
Embodiment 2.
A fuel cell system according to embodiment 2 will be described. Fig. 6 is a system diagram showing the structure of the fuel cell system according to the present embodiment. Fig. 7 is a cross-sectional view showing an internal structure of the vapor generator in the fuel cell system according to the present embodiment. The present embodiment differs from embodiment 1 in that the auxiliary heating apparatus 303 includes an auxiliary burner 50 and a combustion exhaust gas flow path 314. The same reference numerals are given to constituent elements having the same functions and actions as those of embodiment 1, and the description thereof will be omitted.
As shown in fig. 6 and 7, an auxiliary burner 50 is provided at the upper portion of the steam generator 4. The auxiliary burner 50 forms part of an auxiliary heating 303. The auxiliary burner 50 is disposed on the central axis 4a of the steam generator 4. The auxiliary burner 50 is opposed to the anode off-gas flow path 302 with the evaporation flow path 301 interposed therebetween.
The auxiliary combustion fuel system 216 branches into an auxiliary combustion fuel system 217 and an auxiliary combustion fuel system 218. The auxiliary combustion fuel system 217 is connected to the burner 3. The auxiliary combustion fuel system 218 is connected to the auxiliary burner 50. The auxiliary combustion fuel F16 flowing through the auxiliary combustion fuel system 216 is split into an auxiliary combustion fuel F17 and an auxiliary combustion fuel F18. The auxiliary combustion fuel F17 is supplied to the burner 3 through the auxiliary combustion fuel system 217. The auxiliary combustion fuel F18 is supplied to the auxiliary burner 50 in communication with the auxiliary combustion fuel system 218.
Between the auxiliary burner 50 and the outside of the steam generator 4, a combustion exhaust gas flow path 314 is provided. The combustion exhaust gas flow path 314 is disposed on the inner peripheral side of the inner peripheral space 42. The combustion exhaust gas flow path 314 and the inner peripheral space 42 are partitioned by a partition wall 315. The partition 315 is formed in a cylindrical shape centering on the central axis 4 a. The combustion exhaust gas flow path 314 is thermally connected to the evaporation flow path 301 via the partition 315, the heat transfer promoting member 306, and the heat transfer pipe 301 a.
The combustion exhaust gas flow path 314 forms part of the auxiliary heating 303. The combustion exhaust gas flow path 314 faces the anode exhaust gas flow path 302 across the evaporation flow path 301.
In the auxiliary burner 50, the auxiliary combustion fuel F18 and combustion-supporting gas such as air are ignited by an igniter or the like and burned, and high-temperature combustion exhaust gas is generated. The high-temperature combustion exhaust gas passes through the combustion exhaust gas flow path 314, and supplies heat energy to the circulating water F10 flowing through the evaporation flow path 301. The combustion exhaust gas after the heat energy is supplied to the circulating water F10 is discharged to the outside of the steam generator 4. The heat of the combustion exhaust gas is controlled by adjusting the flow rate of the auxiliary combustion fuel F18. The other operations are the same as those of embodiment 1.
Regarding the supply of the combustion-supporting gas to the auxiliary burner 50, the auxiliary burner 50 may be configured to introduce the air by natural aspiration. In this case, although it is difficult to change the combustion air ratio, the structure of the auxiliary burner 50 is simplified. The auxiliary burner 50 may be supplied with air via an air supply system provided separately. In this case, by controlling the flow rate ratio of the auxiliary combustion fuel F18 and the air, an arbitrary combustion air ratio can be obtained. This can control the adiabatic flame temperature, so that the amount of movement of heat energy into the circulating water F10 can be more reliably controlled.
According to the present embodiment, in addition to the effects obtained by embodiment 1, the following effects are obtained. That is, in the present embodiment, the auxiliary burner 50 is used in the auxiliary heating device 303, so that the heat energy required for the vapor generator 4 can be generated by using the raw material F00 required for the fuel cell stack 1. Therefore, the fuel cell system 100 can be made efficient.
In the present embodiment, since the auxiliary burner 50 is used in the auxiliary heating apparatus 303, the power consumption at the time of starting the fuel cell system 100 can be suppressed, in particular, as compared with a configuration in which an electric heater is used in the auxiliary heating apparatus 303. Therefore, the fuel cell system 100 can also be applied to an emergency power supply. In addition, the operation at the time of starting the fuel cell system 100 will be described in embodiment 3 described later.
As described above, in the fuel cell system 100 according to the present embodiment, the auxiliary heater 303 includes the auxiliary burner 50 and the combustion exhaust gas flow path 314 through which the combustion exhaust gas generated by the auxiliary burner 50 flows. According to this structure, the power consumption in the auxiliary heating apparatus 303 can be suppressed.
Embodiment 3.
A fuel cell system and an operation method thereof according to embodiment 3 will be described. The present embodiment mainly relates to the operation at the time of starting the fuel cell system 100. Fig. 8 is a system diagram showing the structure of the fuel cell system according to the present embodiment.
As shown in fig. 8, a stack temperature sensor 22 is provided in the fuel cell stack 1. The stack temperature sensor 22 is configured to detect a representative temperature of the fuel cell stack 1. The reformer 2 is provided with a reformer temperature sensor 24. The reformer temperature sensor 24 is configured to detect a representative temperature of the reformer 2. The other structures are the same as those of embodiment 1 shown in fig. 1 and 2.
The operation of the fuel cell system 100 performed by the control of the control unit 90 at the time of starting the fuel cell system 100 will be described. First, the oxidizing agent F03 discharged from the blower 18 flows through the oxidizing agent system 203, passes through the oxidizing agent heat exchanger 7 and the cathode 1c, and is supplied to the combustor 3 as a cathode off-gas F04. A part of the raw material F00 flows through the auxiliary combustion fuel system 216, and is supplied to the burner 3 as the auxiliary combustion fuel F16. In the combustor 3, the cathode off-gas F04 and the auxiliary combustion fuel F16 are ignited by an igniter or the like and burned to generate combustion gas.
The combustion gas generated by the burner 3 heats the reformer 2 and the oxidizer heat exchanger 7, and is discharged as the combustion exhaust gas F15 through the combustion exhaust gas system 215. The oxidant F03 heated in the oxidant heat exchanger 7 is supplied to the cathode 1c, and the sensible heat of the oxidant F03 itself heats the fuel cell stack 1.
In parallel with the above-described process, energization of the auxiliary heating 303 is started. Here, the auxiliary heating device 303 according to the present embodiment is an electric heater. By energizing the auxiliary heating 303, the vapor generator 4 is warmed.
When the temperatures of the fuel cell stack 1 and the reformer 2 are raised to a temperature at which water vapor does not condense, for example, 150 ℃, the water pump 8 is started to supply the circulating water F10 to the vapor generator 4. The circulating water F10 flows from above to below through the evaporation flow path 301 by the discharge pressure of the water pump 8 and gravity. The circulating water F10 flowing through the evaporation flow path 301 is evaporated by receiving heat from the auxiliary heating device 303, and becomes water vapor F11. The steam F11 is supplied to the reformer 2 and the anode 1a by the injector 9 as the fuel gas F02 at the time of starting.
The anode off-gas F06 discharged from the anode 1a flows through the anode off-gas flow path 302 of the steam generator 4 from below to above, and flows out from the anode off-gas flow path outlet 308.
During the temperature increase of the vapor generator 4, the anode off-gas F06 is in a state rich in water vapor. When a low temperature portion is present in the anode off-gas flow path 302, water vapor in the anode off-gas F06 condenses. However, even when the water vapor in the anode off-gas F06 is condensed, the condensed water is accumulated in the condensed water accumulation space 304 provided in the lower portion of the anode off-gas flow path 302, and is discharged through the condensed water discharge pipe 305.
When the temperature of the reformer 2 increases to a temperature at which hydrogen can be produced by the reforming reaction by the reforming catalyst filled into the reformer, for example, 450 ℃, the supply of the raw material F01 by the raw material system 200 and the reforming raw material system 201 is started. The flow rate of the raw material F01 at the start of supply is controlled in consideration of S/C. The value of S/C in the rated operation state is, for example, in the range of 2.5 to 3.5. In contrast, the flow rate of the raw material F01 at the start of supply is set to a value of S/C greater than that in the rated operation state. In the reformer 2 at the time of start-up, a transitional temperature distribution is formed. In order to prevent carbon (C) from being deposited in the reformer 2 due to this temperature distribution, the flow rate of the raw material F01 at the start of supply is set to, for example, about 8.0S/C. Thereafter, the flow rate of the water vapor F11 and the flow rate of the raw material F01 are appropriately controlled.
The supply of the raw material F01 is started before the temperature of the fuel cell stack 1 rises to a temperature at which the oxidation reaction of the component parts constituting the fuel cell stack 1 proceeds, for example, 300 ℃. That is, the supply of the raw material F01 is started under the temperature conditions that the temperature of the reformer 2 is 450 ℃ or higher and the temperature of the fuel cell stack 1 is 300 ℃ or lower. In order to achieve this temperature condition, the combustion temperature of the burner 3 and the input energy of the burner 3 are controlled by adjusting the flow rate of the auxiliary combustion fuel F16 supplied to the burner 3 and the flow rate of the oxidizing agent F03 supplied to the burner 3 as the cathode off-gas F04.
The flow rates of the oxidizing agent F03, the raw material F01, and the water vapor F11, which are gases required for the battery reaction, are set to predetermined flow rates. The fuel cell stack 1 is warmed up to a temperature at which power generation is possible, for example, 600 ℃. After the temperature of the fuel cell stack 1 is raised to a temperature at which power generation is possible, the flow rates of the oxidant F03, the raw material F01, and the steam F11 are controlled to predetermined flow rates. In parallel with this, power generation is started in the fuel cell stack 1 by a method such as current control or power control, and the fuel cell system 100 shifts to a predetermined rated operation state.
As the temperature of the fuel cell stack 1 increases, the flow rate of the anode off-gas F06 increases, and the temperature of the anode off-gas F06 increases. Thereby, the enthalpy of the anode off-gas F06 becomes large. Accordingly, in the steam generator 4, the heat energy supplied from the anode off-gas F06 to the circulating water F10 increases.
The control unit 90 controls the auxiliary heating device 303 based on the temperature of the anode off-gas F06 detected by the anode off-gas temperature sensor 21. Specifically, the control unit 90 controls the auxiliary heating device 303 so that the amount of heat generated by the auxiliary heating device 303 decreases as the temperature of the anode off-gas F06 increases. Thereby, as the temperature of the anode off-gas F06 increases, the amount of heat generated by the auxiliary heating device 303 decreases. Therefore, the circulating water F10 can be prevented from being supplied with heat energy more than necessary. In this way, the heat energy supplied to the circulating water F10 is regulated.
Alternatively, the control unit 90 may control the auxiliary heating device 303 based on the temperature of the water vapor F11 detected by the water vapor temperature sensor 20. Specifically, the control unit 90 controls the auxiliary heating device 303 so that the amount of heat generated by the auxiliary heating device 303 decreases as the temperature of the water vapor F11 increases. In this way, the circulating water F10 can be prevented from being supplied with more heat energy than necessary.
The anode off-gas F06 after passing through the steam generator 4 further provides heat energy to the cooling medium F14 flowing through the heat recovery system 214 in the heat recovery cooler 10. Thereby, the temperature of the anode off-gas F06 flowing into the water separator 5 is reduced to a predetermined temperature below the dew point.
In the water separator 5, the moisture contained in the anode off-gas F06 liquefies according to the saturated vapor pressure at the temperature of the anode off-gas F06. The liquefied moisture is separated from the anode off-gas F06 as water droplets, and is stored in the lower portion of the water separator 5.
On the other hand, the anode off-gas F06 from which the water content has been removed by the water separator 5 flows out of the water separator 5 as the anode recycle gas F07, passes through the anode recycle gas system 207, and reaches the recycle branching portion 221. The anode recycle gas F07 is divided into a recycle combustion gas F08 flowing through the recycle combustion gas system 208 and an anode recycle gas F09 flowing through the anode recycle gas system 209 in the recycle branching portion 221. The recirculated combustion gas F08 is supplied to the combustor 3 through the recirculated combustion gas system 208.
At the time of starting the fuel cell system 100, the auxiliary combustion fuel F16 supplied by the auxiliary combustion fuel system 216 and the cathode off-gas F04 supplied by the cathode off-gas system 204 are mainly combusted in the combustor 3. When the supply of the raw material F01 is started and the flow rate of the raw material F01 increases, the flow rate of the recirculated combustion gas F08 increases, so that the combustion fuel supplied to the combustor 3 increases. Therefore, after starting the supply of the raw material F01, the flow rate of the auxiliary combustion fuel F16, the flow distribution ratio of the recirculated combustion gas F08 in the recovery branch portion 221, and the flow rate of the oxidizing agent F03 are appropriately controlled.
In the present embodiment, the anode recycle gas F07 flowing through the anode recycle gas system 207 is split into the recycle combustion gas F08 and the anode recycle gas F09 in the recycle branching portion 221, but the present invention is not limited thereto. For example, at the time of starting the fuel cell system 100, the entire amount of the anode recycle gas F07 flowing through the anode recycle gas system 207 may be caused to flow through the recycle combustion gas system 208 as the recycle combustion gas F08.
In the present embodiment, the auxiliary heating device 303 is controlled by the control unit 90 so that the supply of the steam F11 to the reformer 2 and the anode 1a is started during a specific period. The specific period is a period after the temperature of the fuel cell stack 1 has risen to the 1 st temperature and before the temperature of the fuel cell stack 1 has risen to the 2 nd temperature. The 1 st temperature is a temperature at which water vapor does not condense in the fuel cell stack 1, for example, 150 ℃. The 2 nd temperature is a temperature at which an oxidation reaction of the component parts constituting the fuel cell stack 1 proceeds, for example, 300 ℃.
In the present embodiment, at the time of starting the fuel cell system 100, the heat energy required for generating the necessary flow rate of the water vapor F11 is supplied from the auxiliary heating device 303 to the evaporation flow path 301. As the temperature increase of the fuel cell system 100 proceeds, the thermal energy supplied from the anode off-gas flow path 302 to the evaporation flow path 301 increases. Therefore, the amount of heat generated by the auxiliary heating device 303 is reduced by the control of the control unit 90. As a result, the heat energy required for generating the steam F11 is supplied to the evaporation flow path 301 from both the auxiliary heating device 303 and the anode off-gas flow path 302. When the fuel cell system 100 is in the rated operation state, the thermal energy supplied from the anode off-gas flow path 302 to the evaporation flow path 301 further increases. Therefore, the auxiliary heating device 303 is stopped by the control of the control unit 90. Thereby, the heat energy required for generating the water vapor F11 is supplied from the anode off-gas flow path 302 to the evaporation flow path 301.
As described above, in the present embodiment, at the time of starting the fuel cell system 100, the temperature can be continuously raised while forming a necessary gas atmosphere. Therefore, according to the present embodiment, stable water vapor generation with less pulsation can be realized according to the temperature rising condition of the fuel cell system 100. Further, according to the present embodiment, the fuel cell system 100 having a high degree of freedom and high energy efficiency can be realized.
Fig. 9 is a cross-sectional view showing an internal structure of the steam generator according to modification 3-1 of the present embodiment. As shown in fig. 9, the vapor generator 4 includes a 1 st flow path member 316 and a 2 nd flow path member 317.
The 1 st flow path member 316 is formed in a cylindrical shape centering on the central axis 4 a. A groove 316a is formed in the outer peripheral surface of the 1 st flow channel member 316. The groove 316a extends in a spiral shape with the central axis 4a as a spiral axis.
The 2 nd flow path member 317 is formed in a cylindrical shape centering on the central axis 4 a. The 2 nd flow path member 317 has an inner diameter equal to the outer diameter of the 1 st flow path member 316. The inner peripheral surface of the 2 nd flow path member 317 is joined to the outer peripheral surface of the 1 st flow path member 316.
Inside the groove 316a, an evaporation flow path 301 is formed. An evaporation channel inlet 301b is provided at the upper end of the evaporation channel 301. An evaporation channel outlet 301c is provided at the lower end of the evaporation channel 301.
The 1 st flow path member 316 and the 2 nd flow path member 317 are disposed on the outer peripheral side of the combustion exhaust gas flow path 314 and on the inner peripheral side of the anode exhaust gas flow path 302. The inner peripheral surface of the 1 st flow path member 316 faces the combustion exhaust gas flow path 314. The evaporation flow path 301 is thermally connected to the combustion exhaust flow path 314 via the 1 st flow path member 316. The outer peripheral surface of the 2 nd flow path member 317 faces the anode off-gas flow path 302. The evaporation flow path 301 is thermally connected to the anode off-gas flow path 302 via a 2 nd flow path member 317.
Heat energy is supplied from the combustion exhaust gas flowing through the combustion exhaust gas flow path 314 to the circulating water F10 flowing through the evaporation flow path 301 via the 1 st flow path member 316. Further, heat energy is supplied to the circulating water F10 from the anode off-gas F06 flowing through the anode off-gas flow field 302 via the 2 nd flow field member 317.
According to the present embodiment, heat energy is transferred to the circulating water F10 from both the combustion exhaust gas flowing through the combustion exhaust gas flow path 314 and the anode exhaust gas F06 flowing through the anode exhaust gas flow path 302 via a single member. This reduces the thermal resistance in any heat transfer path, and thus can improve the heat transfer characteristics of the vapor generator 4. Therefore, the small-sized and highly responsive vapor generator 4 can be realized, so that the high-performance fuel cell system 100 can be realized.
As described above, the fuel cell system 100 according to the present embodiment further includes the stack temperature sensor 22 and the control unit 90 that detect the temperature of the fuel cell stack 1. When starting the fuel cell system 100, the control unit 90 controls the auxiliary heating device 303 so that the supply of the steam F11 to the reformer 2 is started during a specific period. The specific period is after the temperature of the fuel cell stack 1 has risen to the 1 st temperature and before the temperature of the fuel cell stack 1 has risen to the 2 nd temperature higher than the 1 st temperature.
In the fuel cell system 100 according to the present embodiment, the 1 st temperature is 150 ℃, and the 2 nd temperature is 300 ℃.
With the above configuration, dew condensation can be prevented from occurring in the fuel cell stack 1. In addition, according to the above configuration, the supply of the water vapor F11 can be started before the oxidation reaction of the component parts constituting the fuel cell stack 1 proceeds.
Embodiment 4.
A fuel cell system and an operation method thereof according to embodiment 4 will be described. The present embodiment mainly relates to the operation of the fuel cell system 100 when it is stopped. The structure of the fuel cell system 100 according to the present embodiment is the same as that of the fuel cell system 100 according to embodiment 3 shown in fig. 8. That is, the fuel cell system 100 according to the present embodiment includes the stack temperature sensor 22 and the reformer temperature sensor 24, similarly to the fuel cell system 100 according to embodiment 3.
The operation of the fuel cell system 100 performed by the control of the control unit 90 when the fuel cell system 100 is stopped will be described. When the fuel cell system 100 is stopped, the control unit 90 decreases the output of the fuel cell stack 1, and stops the power generation of the fuel cell stack 1. The control unit 90 reduces the supply amount of the raw material F01 and stops the supply of the raw material F01 in parallel with the reduction of the output of the fuel cell stack 1 or after the stop of the power generation of the fuel cell stack 1. The control unit 90 starts to operate the auxiliary heating device 303 while the supply amount of the raw material F01 starts to decrease. Here, the auxiliary heating device 303 according to the present embodiment is an electric heater. When the flow rate of the raw material F01 is less than the threshold value, the control unit 90 completely closes the recirculated combustion gas flow rate adjustment valve 311. Thereby, the supply of the recirculated combustion gas F08 to the combustor 3 is cut off, and the combustion in the combustor 3 is stopped.
The water pump 8 maintains an operating state. The circulating water F10 is supplied to the evaporation flow path 301 of the steam generator 4 by the water pump 8. The anode off-gas F06 is supplied to the anode off-gas flow path 302 of the steam generator 4 via the anode off-gas flow path 302. Heat energy is supplied from the anode off-gas flow path 302 and the auxiliary heating device 303 to the circulating water F10 in the evaporation flow path 301. Thus, the steam generator 4 stably generates the steam F11.
At this time, the fuel gas F02 flowing through the fuel gas system 202 is water vapor F11 and the anode recycle gas F09. The fuel gas F02 causes a slight CH in the reformer 2 and the fuel cell stack 1 due to a temperature decrease 4 The reaction is generated but most of H 2 The anode off-gas F06 is supplied to the steam generator 4 as it is. The anode off-gas F06 flowing out from the steam generator 4 is cooled in the heat recovery cooler 10, and flows into the water separator 5. In the water separator 5, the water vapor in the anode off-gas F06 condenses to form condensed water, which is separated from the gas component of the anode off-gas F06.
The gas component of the anode off-gas F06 flows out from the water separator 5 and flows into the anode-recovered gas system 207 as the anode-recovered gas F07. Since the recycle combustion gas flow rate adjustment valve 311 is completely closed, the entire amount of the anode recycle gas F07 is the anode recycle gas F09 as it is.
In the ejector 9, the water vapor F11 generated by the vapor generator 4 serves as a driving fluid, and the anode circulation gas F09 is sucked. The steam F11 and the anode recycle gas F09 flow out of the injector 9 as the fuel gas F02, and are supplied to the reformer 2 and the fuel cell stack 1 through the fuel gas system 202. That is, in the fuel cell system 100 at this point in time, the gas circulation of the anode system is repeated while the generation, supply, and condensation of water vapor are repeated.
The flow rate of the oxidizing agent F03 supplied to the cathode 1c is set to an appropriate flow rate in accordance with conditions such as the cooling rate of the fuel cell stack 1 and the reformer 2. The temperature of each of the fuel cell stack 1 and the reformer 2 is reduced by the movement of sensible heat due to the flow of the oxidizing agent F03.
After the temperature of the fuel cell stack 1 is reduced to a temperature at which the anode 1a is not oxidized and the temperature of the reformer 2 is reduced to a temperature at which the reforming catalyst is not oxidized, the anode system is purged with the oxidizing agent F03 or the atmosphere opening of the ring closure of the anode system is performed. The temperature of the fuel cell stack 1 is obtained from the detection signal of the stack temperature sensor 22. The temperature of the reformer 2 is obtained based on the detection signal of the reformer temperature sensor 24. The control of the control unit 90 causes the oxidizing agent F03 to be introduced into the fuel gas system 202, thereby purging the anode system. In fig. 8, the route for introducing the oxidizing agent F03 into the fuel gas system 202 is not shown. The recirculated combustion gas flow rate adjustment valve 311 is opened under the control of the control unit 90, and the closed-loop atmosphere of the anode system is opened.
In the case where the reforming catalyst and the anode 1a of the reformer 2 are not adversely affected by the raw material F00, the raw material F00 may be introduced into the fuel gas system 202 and the raw material F00 may be used for purging. The anode system may be closed by being cut off from the atmosphere after being washed with the oxidizing agent F03 or the raw material F00.
At this time, the control unit 90 stops the auxiliary heating device 303 and the water pump 8. Thereby, the generation of water vapor is stopped. Through the above process, the fuel cell system 100 is stopped.
In the present embodiment, when the fuel cell system 100 is stopped, the steam generator 4 can generate the steam at a necessary flow rate without starting the burner 3. The generated water vapor circulates in the anode system by the driving force of the ejector 9. That is, the water vapor serves as a medium, and the gas composition immediately after the stop of the fuel cell system 100 is substantially maintained. Therefore, the reformer 2 and the fuel cell stack 1 can be cooled in the reducing atmosphere by using the fuel gas F02 and the reformed gas F05. This can maintain the gas atmosphere in each system of the fuel cell system 100 as it is, and efficiently cool each device of the fuel cell system 100.
As described above, the fuel cell system 100 according to the present embodiment further includes the water separator 5, the recovery branch portion 221, and the recirculated combustion gas flow rate adjustment valve 311. The water separator 5 is configured to separate the anode off-gas F06 into condensed water and an anode recycle gas F07. The recovery branching section 221 is configured to split the anode recovery gas F07 into a recycle combustion gas F08 and an anode recycle gas F09 that are supplied to the combustor 3 thermally connected to the reformer 2. The recirculated combustion gas flow rate adjustment valve 311 is configured to shut off the supply of the recirculated combustion gas F08 to the combustor 3. When the fuel cell system 100 is stopped, the control unit 90 stops generating electric energy in the fuel cell stack 1, closes the recirculated combustion gas flow rate adjustment valve 311, and controls the auxiliary heating device 303 to ensure the flow rate of the steam F11, thereby cooling the reformer 2 and the fuel cell stack 1. Here, the recirculated combustion gas flow rate adjustment valve 311 is an example of a shut-off portion.
With this configuration, the gas atmosphere in each system of the fuel cell system 100 can be maintained as it is, and each device of the fuel cell system 100 can be efficiently cooled.
The fuel cell system 100 according to the present embodiment further includes an anode off-gas temperature sensor 21 that detects the temperature of the anode off-gas F06. The control unit 90 controls the auxiliary heating device 303 based on the temperature of the anode off-gas F06. According to this structure, the circulating water F10 can be prevented from being supplied with heat energy more than necessary.
The fuel cell system 100 according to the present embodiment further includes a water vapor temperature sensor 20 that detects the temperature of the water vapor F11. The control unit 90 controls the auxiliary heating device 303 based on the temperature of the water vapor F11. According to this structure, the circulating water F10 can be prevented from being supplied with heat energy more than necessary.
In the fuel cell system 100 according to the present embodiment, the control unit 90 may open the recirculated combustion gas flow rate adjustment valve 311 after the temperature of the fuel cell stack 1 is reduced to the 2 nd temperature. After the temperature of the fuel cell stack 1 is reduced to the 2 nd temperature, the control unit 90 may introduce the oxidizing agent F03 or the raw material F00 into the anode system, for example, the fuel gas system 202, passing through the reformer 2 and the anode 1 a.
Embodiment 5.
A fuel cell system and an operation method thereof according to embodiment 5 will be described. Fig. 10 is a system diagram showing the structure of the fuel cell system according to the present embodiment.
As shown in fig. 10, the fuel cell stack 1 is provided with a circulation heat exchanger 23. The circulation heat exchanger 23 is disposed between the steam generator 4 of the anode off-gas system 206 and the heat recovery cooler 10 and between the recovery branch 221 of the anode circulation gas system 209 and the ejector 9. The other structure is the same as that of embodiment 2 shown in fig. 6.
In the circulation heat exchanger 23, heat exchange is performed between the anode off-gas F06 flowing through the anode off-gas system 206 and the anode circulation gas F09 flowing through the anode circulation gas system 209. The anode recycle gas F09 obtains heat energy from the anode off-gas F06 flowing out from the vapor generator 4 in the recycle heat exchanger 23. Thereby, the temperature of the anode recycle gas F09 increases.
In the present embodiment, the anode recycle gas F07 immediately after flowing out from the water separator 5 is saturated vapor, whereas the anode recycle gas F09 after passing through the recycle heat exchanger 23 becomes superheated vapor by the heat energy obtained from the anode off-gas F06. Accordingly, dew condensation can be prevented from occurring in the piping from the circulation heat exchanger 23 to the ejector 9 in the anode circulation gas system 209. Therefore, pulsation of the anode recycle gas F09 flowing through the anode recycle gas system 209 is suppressed, and a stable fuel cell system 100 can be realized.
In all of the above embodiments, each structural device of the fuel cell system 100 is surrounded by a heat insulating material. Thereby, heat dissipation from each structural device to the outside is suppressed.
In all of the above embodiments, the total amount of the cathode off-gas F04 is supplied to the combustor 3 to be the combustion-supporting gas, but the present invention is not limited thereto. The cathode off-gas F04 may be branched upstream of the burner 3, and a part of the cathode off-gas F04 may be supplied to the burner 3, and the remaining cathode off-gas may be heated at least one of the reformer 2 and the oxidizer heat exchanger 7. The cathode off-gas F04 may be branched in the combustor 3, and the cathode off-gas F04 may be divided into a gas that burns together with the recirculated combustion gas F08 or the auxiliary combustion fuel F16 and a gas that does not burn. Further, they may be combined. Thus, combustion conditions at an appropriate air ratio can be achieved.
In all of the above embodiments, the timing at which the auxiliary heating device 303 starts to operate and the timing at which the water pump 8 operates are not limited to the above. For example, the auxiliary heating device 303 may be operated according to the heat capacity of each of the fuel cell stack 1, the reformer 2, and the steam generator 4, and the temperature rise state of each of the reformer 2 and the fuel cell stack 1 using the burner 3.
In all of the above embodiments, water can be used as the cooling medium F14 flowing through the heat recovery system 214. However, the cooling medium F14 may be a refrigerant or a heat storage material as long as it can extract heat energy from the anode off-gas F06.
In all of the above embodiments, as the water treatment device 14, for example, an ion exchange device using an ion exchange resin can be used. However, the water treatment device 14 may use a transmissive film or may be a filter according to the specification. In addition, if there is no necessity, the water treatment device 14 may not be provided.
In all the above embodiments, the evaporation flow path 301 is formed in a spiral shape at intervals of every 1 week. However, the evaporation flow path 301 may be formed in a spiral shape closely contacting with each other without any gap. In this case, the heat transfer area per unit length in the axial direction of the vapor generator 4 becomes large, so that the heat transfer performance of the vapor generator 4 improves.
In all of the above embodiments, the condensation temperature of the anode off-gas F06 in the water separator 5 is about 60 ℃. However, the condensation temperature of the anode off-gas F06 in the water separator 5 is not limited thereto, and may be other temperatures. However, the condensation temperature of the anode off-gas F06 in the water separator 5 is preferably set so that the condensation water amount per hour of the anode off-gas F06 in the water separator 5 becomes equal to or higher than the flow rate of the circulating water F10. In this case, after the fuel cell system 100 is started, it is not necessary to supply water to the fuel cell system 100 from the outside. Therefore, the fuel cell system 100 can be independent of water, and the operation cost of the fuel cell system 100 can be reduced.
The above embodiments and modifications can be combined with each other.

Claims (15)

1. A fuel cell system is provided with:
a steam generator for heating water to generate steam;
a reformer configured to react the steam with hydrocarbon to generate a reformed gas containing hydrogen;
a fuel cell stack having an anode and a cathode, generating electric power by an electrochemical reaction of the reformed gas supplied to the anode and an oxidant supplied to the cathode; and
an ejector for supplying at least one of a raw material containing the hydrocarbon and an anode recycle gas obtained by recovering a part of an anode off-gas discharged from the anode to the reformer by using the steam as a driving fluid,
The steam generator has:
an evaporation flow path through which the water flows;
an anode off-gas flow path thermally connected to the evaporation flow path, the anode off-gas flowing through; and
an auxiliary heating device for heating the water,
the anode off-gas flow path and the auxiliary heating device are opposed to each other across the evaporation flow path.
2. The fuel cell system according to claim 1, wherein,
the evaporation flow path extends obliquely to the up-down direction,
in the evaporation flow path, a downward slope is generated from the upstream side toward the downstream side.
3. The fuel cell system according to claim 1 or 2, wherein,
the anode off-gas flow path extends in the up-down direction,
the steam generator has:
a flow path wall extending in the up-down direction and defining the anode off-gas flow path;
an inflow pipe penetrating the flow path wall and connected to the anode off-gas flow path, the anode off-gas flowing in; and
an outflow pipe connected to the anode off-gas flow path above the inflow pipe, the anode off-gas flowing out,
a dew condensation water accumulation space for accumulating dew condensation water is provided below the inflow pipe in the anode off-gas flow path.
4. The fuel cell system according to claim 3, wherein,
the inflow pipe has an end face facing the anode off-gas flow path,
the end face protrudes further toward the inside of the anode off-gas flow passage than the inner wall face of the flow passage wall.
5. The fuel cell system according to claim 3, wherein,
the anode off-gas flow path is provided with a dew condensation water guide plate which guides dew condensation water above the inflow pipe.
6. The fuel cell system according to any one of claims 1 to 5, wherein,
the auxiliary heating device is provided with an electric heater.
7. The fuel cell system according to any one of claims 1 to 5, wherein,
the auxiliary heating device has an auxiliary burner and a combustion exhaust gas flow path through which combustion exhaust gas generated by the auxiliary burner flows.
8. The fuel cell system according to any one of claims 1 to 7, further comprising:
an anode exhaust gas temperature sensor that detects a temperature of the anode exhaust gas; and
the control part is used for controlling the control part to control the control part,
the control unit controls the auxiliary heating device according to the temperature of the anode off-gas.
9. The fuel cell system according to any one of claims 1 to 7, further comprising:
A steam temperature sensor that detects a temperature of the steam; and
the control part is used for controlling the control part to control the control part,
the control unit controls the auxiliary heating device according to the temperature of the water vapor.
10. The fuel cell system according to claim 8 or 9, wherein,
further provided with a stack temperature sensor for detecting the temperature of the fuel cell stack,
the control unit controls the auxiliary heating device so that the supply of the steam to the reformer is started during a specific period when the fuel cell system is started,
the specific period is after the temperature of the fuel cell stack has risen to the 1 st temperature and before the temperature of the fuel cell stack has risen to the 2 nd temperature higher than the 1 st temperature.
11. The fuel cell system according to any one of claims 1 to 7, further comprising:
a stack temperature sensor that detects a temperature of the fuel cell stack; and
the control part is used for controlling the control part to control the control part,
the control unit controls the auxiliary heating device so that the supply of the steam to the reformer is started during a specific period when the fuel cell system is started,
the specific period is after the temperature of the fuel cell stack has risen to the 1 st temperature and before the temperature of the fuel cell stack has risen to the 2 nd temperature higher than the 1 st temperature.
12. The fuel cell system according to claim 10 or 11, wherein,
the 1 st temperature is 150℃and the 2 nd temperature is 300 ℃.
13. The fuel cell system according to any one of claims 10 to 12, further comprising:
a water separator separating the anode off-gas into condensed water and an anode recycle gas;
a recovery branching portion that branches the anode recovery gas into a recirculated combustion gas and the anode circulation gas that are supplied to a combustor thermally connected to the reforming portion; and
a shutoff unit configured to shut off supply of the recirculated combustion gas to the combustor,
the control unit stops generating the electric energy in the fuel cell stack when the fuel cell system is stopped, closes the shut-off unit, and controls the auxiliary heating device to ensure the flow rate of the steam, thereby cooling the reformer and the fuel cell stack.
14. The fuel cell system according to claim 13, wherein,
the control unit opens the shut-off unit after the temperature of the fuel cell stack has decreased to the 2 nd temperature.
15. The fuel cell system according to claim 13 or 14, wherein,
The control unit introduces the oxidizing agent or the raw material into the anode system passing through the reformer and the anode after the temperature of the fuel cell stack is reduced to the 2 nd temperature.
CN202180097869.0A 2021-05-11 2021-05-11 fuel cell system Pending CN117296172A (en)

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